The present invention relates to making parts out of composite material, and more particularly to making reinforcing fiber structures for such parts.
A particular field of application of the invention lies in making parts of structural composite material, i.e. parts having a fiber reinforcing structure that is densified by a matrix. Composite materials make it possible to fabricate parts that present overall weight that is less than that of the same parts when made of metal.
In the context of making fiber structures by multilayer weaving so as to produce the fiber reinforcement for a composite material part, such as a blade for an aeroengine, it is necessary during weaving of the structure to withdraw yarns both in the warp direction and in the weft direction in order to match reductions in the thickness of the part, e.g. in the fastening or in the trailing edge of the blade, so as to obtain a fiber preform that presents the quasi-final shape and dimensions of the blade (i.e. that presents its “net shape”). Withdrawing yarns in this way during weaving gives rise to non-woven yarns being present locally at the surface of the fiber structures (i.e. to yarns that are floated), which yarns are subsequently cut during a second operation.
Cutting these fibers at the surface of the structure gives rise locally to fiber misalignments and consequently, once the matrix has been deposited, to zones in the part that are rich in matrix material, which zones are potential sources of microcracking in the material of the part.
In addition, because of the weave present at the surface of the fabric, e.g. a satin weave, all of the floated yarns present after the last interlinking point of the yarn that has been extracted from the fiber need to be cut, thereby giving rise locally to a significant variation in the density of fibers.